Materials and methods for the control of plant pathogens

ABSTRACT

The subject invention provides compositions useful for the control of plant pathogens. Specifically exemplified are essential oil compositions which are effective in the control of fungal and bacterial plant pathogens.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from provisional patent applicationsU.S. Ser. No. 60/288,469, filed May 31, 2001 and U.S. Ser. No.60/223,903, filed Aug. 9, 2000.

BACKGROUND OF THE INVENTION

Plants are subject to attack by a great number of pathogens. Thesepathogens can be, for example, bacteria, fungi, or nematodes. Pesticidalcompounds have long been used to increase yields and extend agriculturalproduction capabilities into new areas. They have also been extremelyimportant tools for ameliorating season-to-season differences in yieldand quality caused by weather-driven variations in disease pressure.

The future role of pesticides in agriculture is increasingly threatenedby several factors including; the development of pest resistance,increasing concerns about food safety, and environmental accumulation oftoxic compounds. As older pesticides are removed from the market due toregulatory changes, and new pesticides are becoming increasinglyexpensive to register, there is an increasing need to find ways to morewisely use the remaining, safest pesticides. This is particularly truefor the many crop/disease combinations which do not represent largeenough markets to pay for the cost of new compound registration. Wiserpesticide use will include ways to reduce application rates (and thuspotential residues), finding ways to extend registrations to new crops,and identifying new compositions and treatments to combat thedevelopment of pest resistance.

Chemical pesticides have provided an effective method of control;however, the public has become concerned about the amount of residualchemicals which might be found in food, ground water and theenvironment. Stringent new restrictions on the use of chemicals and theelimination of some effective pesticides from the market place couldlimit economical and effective options for controlling pests. Inaddition, the regular use of chemical toxins to control unwantedorganisms can select for resistant strains.

Alternative strategies to pesticide application are needed for thecontrol of agriculturally important pests. Such strategies will helpaddress public concern regarding pesticide pollution, as well as theperception that pesticide residues on food pose a threat to humanhealth.

Among the more destructive zoosporic plant pathogens are the downymildews (which are primarily associated with severe foliar diseases ofmany crops), and numerous species in the genus Pythium and Phytophthorawhich are destructive pathogens of roots, foliage, and fruits. Withinthe fungal genus Pythium are plant pathogenic species which can causesignificant losses in vegetable production.

The value of vegetable crops grown in the state of Florida totaled over$1.79 billion for the 1991–92 crop season with much of the cabbage,cucumber, pepper, and tomato crops planted as transplants. Tomato aloneaccounts for $735 million in this production total and over 80% of thecrop is transplanted. The use of vegetable transplants in commercialfield production systems is important in many areas of the UnitedStates. In California, all of the celery, fresh market tomato andpepper, and most of the cauliflower and broccoli are grown as transplantcrops. In Monterey County alone, the value of the transplants grown in1992 amounted to nearly $18 million and represented a final crop valueof $176 million.

Plant pathogenic Pythium species can kill a plant at the seedling stageor can reduce crop yield by destroying the root system of a matureplant. While diseases in the seedling stage are often controlled byfungicide application, the continued use of certain highly effectivefungicides, e.g., metalaxyl, has faced regulatory uncertainty for use invegetable transplant greenhouse production systems. In addition,continued use of a particular fungicide can result in the development oftolerance by the pathogen. Fumigants such as methyl bromide, which areroutinely used on high cash-value crops, also face regulatoryuncertainty. Thus, disease control (in particular damping-off) in theproduction greenhouses as well as in the field following transplantingare a major concern.

An alternative to the use of chemical pesticides for controllingphytopathogenic Pythium spp. is the use of biological control agents forvegetable transplants, a large and expanding industry in which diseaseprotection is needed in the greenhouse as well as in the field aftertransplanting.

U.S. Pat. No. 4,574,083 to Baker and Lifshitz describes Pythium nunn,which is not pathogenic to plants and can protect seedlings fromdamping-off in greenhouse evaluations.

There are a number of studies examining the effect of seed treatmentwith oospores of P. oligandrum on reducing subsequent levels of disease,most of which have been conducted in the greenhouse. Deacon (1976;Trans. Br. Mycol. Soc. 66:383–391) described the ability of mycelialseed coatings on wheat to significantly reduce the disease incidenceover untreated seeds.

Vesely (1977; Phytopath Z. 90:113–115; 1979) observed that applicationof oospores to sugarbeet seed reduced damping-off incidence to a similarlevel as thiram treatment (see also Schippers, B. and W. Gams, eds.Academic Press, Soil-Borne Plant Pathogens). In U.S. Pat. No. 4,259,317,Vesely et al. describe the application of Pythium oligandrum, or“Polygandron.”

Bacterial wilt caused by Ralstonia solanacearum (Rs) is a major diseaseproblem in fresh tomato production fields in north Florida. Fusarium isalso an important plant pathogen.

Damage to plants caused by nematodes is also a prevalent and seriouseconomic problem. Nematodes cause wide-spread and serious damage in manyplant species. Many genera of nematodes are known to cause such damage.Plant-parasitic nematodes include members of the Phylum Nematoda, OrdersTylenchida and Dorylaimide. In the Order Tylenchida, the plant-parasiticnematodes are found in two Super Families: Tylenchoidea andCriconematoidea. There are more than 100,000 described species ofnematodes.

Currently, the most effective substance for soil treatment is methylbromide. Methyl bromide is used in the control of pest insects,nematodes, weeds, pathogens, and rodents. In the United States, about27,000 tons of methyl bromide is used annually in agriculture, primarilyfor soil fumigation, as well as for commodity and quarantine treatment,and structural fumigation. Globally, about 76,000 tons of methyl bromideare used each year.

When used as a soil treatment, methyl bromide is injected into the soilat a depth of 12 to 24 inches before a crop is planted. This willeffectively sterilize the soil, killing the vast majority of soilorganisms. Immediately after the methyl bromide is injected, the soil iscovered with plastic tarps that hold most of the methyl bromide in thesoil. The tarps are removed 24 to 72 hours later.

After the tarps are removed, much of the methyl bromide leaves the soil.The EPA estimates that about 50% to 95% of the methyl bromide in thesoil eventually enters the atmosphere.

While methyl bromide in large doses can result in damage to the humannervous system and respiratory system, the greatest danger poised bymethyl bromides is the damage to the ozone layer. According to the 1994Assessment of Ozone Depletion, the Ozone Depletion Potential (ODP) ofmethyl bromide has been assessed to be 0.6. This makes the ODP of themethyl bromide fifty times more effective at destroying ozone than CFC'son a per molecule basis.

According to the Clean Air Act (1990 Amendments), all substances with anODP of 0.2 or greater are to be phased out in the United States. Thismeans that methyl bromide will need to be phased out. There has beenlegislation to ultimately prohibit the production and importation ofmethyl bromide in the United States. In addition, 160 countries havesigned the Montreal Protocol, a treaty calling for the levels ofozone-depleting chemicals to be frozen at 1991 levels. Finally, the EPAis lobbying for nations to stop using methyl bromide all together.

In light of the environmental problems with methyl bromide, and thecontinuing need for a soil treatment, an environmentally safe chemicalalternative has been sought. Thus, there remains a need for pathogencontrol methods which are more compatible with the need for affordableand effective disease control, a high degree of food safety, and minimalenvironmental impact.

BRIEF SUMMARY OF THE INVENTION

The subject invention provides essential oils that can be used for thecontrol of plant pathogens. Advantageously, the subject inventionprovides fumigants that provide an alternative to methyl bromide andother pre-plant fumigants. According to the subject invention, in apreferred embodiment essential oils can be used to control bacterial andfungal soilborne diseases of vegetables, ornamental plants and otherplants.

Specifically exemplified herein are essential oils from the followingplants: Palmarosa (Cymbopogon martini), tea tree (Melaleucaalternifolia), lemongrass (Cymbopogon flexuosus) and Eucalyptuscitriodora. Additionally, thymol which is a fraction of thyme (Thymusvulgaris) oil was found effective to control plant diseases.

In a specific embodiment of the subject invention, geraniol, which is afraction of palmarosa, can be used to effectively control plantpathogens. Specifically, exemplified herein is the use of geranioland/or palmarosa oil against the bacterial wilt pathogen.

The essential oils of the subject invention and their derivatives arehighly advantageous for pesticidal use because they occur commonly innature, have little mammalian toxicity, are compatible with otherbiological control strategies and are readily broken down to innocuouscomponents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the effect of selected essential oils on colony developmentof Ralstonia solanacearum.

FIG. 2 shows the effect of thymol on the colony development of Ralstoniasolanacearum.

DETAILED DISCLOSURE OF THE INVENTION

The subject invention concerns unique materials and methods for theeffective and environmentally safe control of plant pathogens. In eachembodiment of the subject invention, plant essential oil compositionsconstitute a critical component of the control strategy. As described indetail below, the essential oil component may be a salt or derivative.As used herein, reference to “essential oil” should be understood toinclude salts and derivatives thereof.

A description of essential oils can be found at, for example, Guenther,Ernest, The essential oils (1972) Hungtington, N.Y., R.E. Krieger Pub.Co., which is incorporated herein by reference.

Essential oils of tea tree (Melalcuca alternifolia), marjoram (Thymusmasiichina), oregano (Origanum vulgure), thyme (Thymus vulgaris) andpalmarosa (Cynbopogon martini) were tested in vitro and in greehousegrown tomatoes for their efficacy against Ralstonia solenacearum (Rs).Also thymol, one of the fractions of thyme oil, was tested in vitro andin greenhouse. Thymol, the vapor effect of palmarosa and thyme essentialoils are effective against Rs. Geraniol has also been found to beeffective for the control of plant pathogens. In a preferred embodimentof the subject invention, essential oils can be integrated into themanagement of bacterial wilt and nematodes (such as Meloides sp.) ontomato.

Advantageously, the chemical compositions used according to the subjectinvention are environmentally safe. The active ingredients in thecompositions are all plant extracts or are derived from plant extracts.In one embodiment, the compositions may comprise a surfactant that actsas a wetting agent. The wetting agent helps during the dilution of thechemical compositions in water. The wetting agent also helps thechemical composition saturate the soil. Preferably, a food gradesurfactant can be used due to the use of the compositions as soil orplant treatments. An example of a suitable surfactant is polysorbate.The amount of surfactant can be readily determined by a person skilledin the art and should be sufficient to set fully the treated soil whenthe first dosage of composition is applied. This amount may change withsoil composition and crop type. The balance of the composition can becompleted with oil and water, and other compounds as appropriate.

The compositions and methods described herein can be used to control abroad range of fungal and bacterial targets. These targets include, butare not limited to species of Penicillium (i.e., expansum, digitatum,italicum), Ralstonia sp., Botrytis sp., Monilinia sp., Alternaria sp.,Aspergillus sp., Rhizopus sp., members of the Erisyphales (powderymildews Sphaerotheca sp., Erisyphe sp., Uncinula sp., Podosphaera sp.),members of the Peronosporales (downy mildews, Phytopthora sp., Pythiumsp., Peronospora sp.) Hemibasidiomycetes (rusts and smuts), Venturiasp., Cercospora sp. Pseudocercosporella sp., Cercospora sp.,Cercosporidium sp., Fusarium sp., Ophiostoma sp. and other wood stainingfungi, and Diplodia sp., other targets include Erwinia sp., Pseudomonassp., and Xanthomonas sp, and nematodes (including Meloides sp.).

These plant pests can be controlled on seeds, corms, bulbs, flowers,stems, leaves, exposed roots, and fruits of plants including, but notlimited to, grapes, pears, apples, peaches, nectarines, grapefruit,cherries, apricots, lemons, oranges, mangos, bananas, and tangerines.The plants which may be treated further include, but are not limited to,potatoes, tomatoes, cucumbers, lettuce, rice, wheat, rye and othercereals, flower crops, and almonds.

As used herein, the term “produce” includes, but is not limited to, anyof the plant surfaces listed above. Also, as used herein, the term“citrus” refers to fruits such as oranges, lemons, limes, grapefruit,and the like.

The compositions can also be applied to surfaces such as freshly cutlumber for the control of fungal or bacterial targets. The compositionsof the subject invention can be used to control microbial plant diseaseon both dormant and non-dormant plant tissue. As known by those skilledin the art, non-dormant tissue includes growing vegetation and fruits(pre- and post-harvest).

In cases where essential oils are useful for eradication of existinginfections of fruit, the further protection of that fruit fromsubsequent infections can be achieved by the simultaneous or subsequentapplication of a fungicide, bactericide, or a biological controlorganism in a dip or spray application. This application can also bemade along with the application of various waxes or finishes which arecommonly used with fruit. The formulation of such applications can alsoinclude nutrients which will benefit the establishment of the biocontrolorganism.

Appropriate formulations and concentrations can be readily ascertainedby those skilled in this art using the teachings of the subjectinvention.

The potent, activity of the compositions of the subject inventioncombined with other fungicides or bactericides makes it possible toachieve the same level of control while using a smaller quantity of thenon-oil fungicide or bactericide component of the mixture. Thecompositions of the present invention can comprise a mixture ofcomponents wherein the mixture is sufficiently active so thatapplication of the composition enables utilization of reduced amounts ofeach of the active ingredients while still providing effective activity.This is significant because lower use rates lead to lower residues onthe crop or in the environment, lower costs of application, an expansionof the margin between crop safety and efficacy for fungicides which canbe phytotoxic (thus enhancing their safety or expanding the crops,varieties or timings for their use), and lower total “market basket”exposure for a multi-use fungicide or bactericide.

Combinations of other fungicides or bactericides with essential oilsoffer additional advantages because of the particular mode of action ofthese materials. One such advantage is a reduction in selection pressurefor resistant forms.

Chemical control agents which can be combined with essential oilsaccording to the subject invention include, but are not limited to,benomyl, borax, captafol, captan, chlorothalonil, various formulationscontaining copper; various formulations containing zinc; dichlone,dicloran, iodine, various ergosterol biosynthesis inhibiting fungicidesincluding but not limited to fenarimol, imazalil, myclobutanil,propiconazole, prochloraz, terbutrazole, flusilazole, triadimefon, andtebuconazole; folpet, iprodione, mancozeb, maneb, metalaxyl,oxycarboxin, oxytetracycline, PCNB, pentachlorophenol, quinomethionate,sodium arsenite, sodium DNOC, sodium hypochlorite, sodium phenylphenate,streptomycin, sulfur, thiabendazole, thiophanate-methyl, triforine,vinclozolin, zineb, ziram, tricyclazole, cymoxanil, blasticidin, andvalidimycin. The essential oils can also be combined with various sprayoils.

Biological control agents that can be used according to the subjectinvention include but are not limited to Bacillus sp., Pseudomonas sp.,Trichoderma sp., Erwinia sp., Pichia sp., Candida sp., Cryptococcus sp.,Talaromyces sp., P. fumosoreus, B. bassiana, Chaetomium sp., Gliocladiumsp., Aureobasidium sp., Dabaryomyces sp., Exophilia sp., Ampelomycessp., and Mariannaea sp.

The invention also encompasses several methods for the treatment ofsoil. In one embodiment, the method involves diluting a concentratedsolution in water. The diluted solution is then sprayed into the groundto a depth of 12 to 24 inches. The amount sprayed is the quantitynecessary to saturate the soil. This amount is between typically about1%–20% by weight of the soil being treated. The amount depends on thetype of soil being treated and the crop being grown.

Among the further applications of the subject invention are thefollowing:

-   -   the use of an essential oil to improve or compliment the        activity of other fungicidal and bactericidal chemicals;    -   the use of an essential oil to provide control and to also        perturb the plant surface microflora to enhance the subsequent        colonization of that surface by a compatible biological control        agent;

Following are examples which illustrate procedures for practicing theinvention. These examples should not be construed as limiting. Allpercentages are by weight and all solvent mixture proportions are byvolume unless otherwise noted.

Example-1

The essential oils tested showed volatile bactericidal activities invitro against Ralstonia solanacearum. Essential oil from palmarosashowed the greatest inhibition of colony development (FIG. 1). Thymol at100 μg/ml concentration entirely inhibited the development of R.solanacearum colonies (FIG. 2). In greenhouse tests, essential oils fromthyme, palmarosa and wild marjoram resulted in significantly lessdisease than the inoculated untreated control (Table 1).

TABLE 1 Effect of essential plant oils and medicinal plants on bacterialwilt of tomato in greenhouse experiments. Experiment 1 Experiment 2Treatments % Severity^(x) % Severity^(x) Untreated Control 80A 100A WildMarjoram EO^(z) 0B —^(y) Thyme EO 0B —  Palmarosa EO 0B  20BNon-inoculated 0B  0B ^(z)EO, essential oil; fresh, fresh plant materialfrom leaves ^(y)—, not tested ^(x)Treatments followed by the same letterdid not differ significantly at P = 0.01 level as determined by LSDrange test.

Example-2

The efficacy of several essential oils were evaluated for management ofthe following soilborne fungi pathogens: Fusarium oxysporum f. sp.lycopersici, Phytophthora capsici, Pythium aphanidermatum, and Atheliarolfsii. In greenhouse tests using microwaved soil infested with fungalpathogens, infection of tomato roots and subsequent root rot caused bythe four fungi was reduced or eliminated in soil treated before plantingwith palmarosa oil and, for P. capsici and A. rolfsii, by oils of wildmarjoram and thyme (Table 2). Root weights generally were greater insoil infested with the four fungi and treated with palmarosa oil than inthe infested, nontreated soil (Table 2). In conclusion, essential oilscan be used as bio-fumigants for integrated management programs againstsoilborne pathogens of tomato and other host plants.

TABLE 2 Fresh weights of shoots and root systems, percentages ofinfection of ‘Bonnie Best Improved’ tomato roots, and plant mortalityafter inoculation^(V) Surviving Plants at Harvest^(X) Root Disease^(W)Shoot Weight Root Weight Pathogen Essential Oil Infection (%) Mortality(%) Rating No. (g) (g) Uninfested wheat seed Water 100^(Y) 0 1.0a^(Z) 616.827a 6.177a Uninfested wheat seed Wild Marjoram 100 0 1.0a 6 16.180ab5.041ab Uninfested wheat seed Palmarosa 83 0 1.0a 6 13.086abcd 4.617abcUninfested wheat seed Red Thyme 100 0 1.0a 6 14.741abc 5.932a Fusariumoxysporum f. sp. lycopersici Water 100 67 2.5cde 2  2.078i 0.238fFusarium oxysporum f. sp. lycopersici Wild Marjoram 100 67 2.0bc 2 4.376hi 0.288f Fusarium oxysporum f. sp. lycopersici Palmarosa 100 01.0a 6 11.526bcde 4.603abc Fusarium oxysporum f. sp. lycopersici RedThyme 33 50 1.7b 3 12.759fg 2.344e Phytophthora capsici Water 100 02.8de 6 11.685bcde 3.267cde Phytophthora capsici Wild Marjoram 0 0 1.0a6 16.856a f.f92ab Phytophthora capsici Palmarosa 0 0 1.0a 6 11.301cde4.504abc Phytophthora capsici Red Thyme 0 0 1.0a 6 15.677abc 5.587abPythium aphanidermatum Water 100 0 3.3e 6  8.193ef 2.826de Pythiumaphanidermatum Wild Marjoram 100 0 2.5cde 6 12.387abcd 4.129bcd Pythiumaphanidermatum Palmarosa 0 0 1.0a 6 12.604abcd 5.592ab Pythiumaphanidermatum Red Thyme 100 0 2.2bcde 6 14.477abc 5.024ab Atheliarolfsii Water 83 33 2.0bc 4  8.437fgh 1.999e Athelia rolfsii WildMarjoram 0 0 1.0a 6 14.819abc 5.589ab Athelia rolfsii Palmarosa 0 0 1.0a6  9.206def 4.082bcd Athelia rolfsii Red Thyme 0 17 2.0bc 5  4.312ghi2.351e ^(V)Three-week-old tomato seedlings were grown in Boynton Beachsoil which had been infested with the pathogen and the oil on 4-16-99 inclosed bags, moved to the greenhouse and placed in pots in 4-19-99, andplanted on 4-21-99. ^(W)Root disease based on an index with 0 = no rootsymptoms; 1 = less than 25% of root tips necrotic; 2 = 25–50% of roottips necrotic; 3 = 50–100% of root tips necrotic plus localized necroticlesions on the tap root or crown; 4 = extensive root rot with few or nowhite roots, crown rot extensive; 5 = root system completely necroticand plant dead or moribund. ^(X)Average fresh weights of shoots androots of plants in each treatment at final havest on 5-19-99 and5-20-99. ^(Y)Fusarium olysporum recovered from control plants.^(Z)Values followed by the same letters in a column are not differentaccording to Duncan's Multiple Range Test (P ≦ 0.05).

Example 3 Use of Geraniol to Control Plant Pathogens

In accordance with the subject invention, geraniol has been shown tohave volatile bactericidal activity against Ralstonia solanacearum.Geraniol reduced population of Ralstonia solanacearum signicantly(89.5%) compared to untreated control. Its effect was compared withpalmarosa oil. In the same experiment, palmarosa oil reduced thepopulation of Ralstonia solanacearum by 87.5%. Thus, geraniol was foundto be highly effective against the bacterial wilt pathogen.

The efficacy of geraniol was also evaluated for management of thefollowing soilborne fungi pathogens: Fusarium oxysporum f. sp.lycopersici, Phytophthora capsici, Pythium aphanidermatum, and Atheliarolfsii. In greenhouse tests using microwaved soil infested with fungalpathogens, infection of tomato roots and subsequent root rot caused bythe four fungi was reduced or eliminated in soil treated before plantingwith geraniol. It was found that the effect of the geraniol is better,or equal to, the effect that is obtained with thymol. Thus, geraniol canbe used effectively as a bio-fumigant for integrated management programsagainst soilborne pathogens of tomato and other host plants (includingvegetables and ornamentals).

Example 4 General Formulations

A. Wettable powders. Wettable powders are water-dispersable compositionscontaining the active material, an inert solid extender, and one or moresurfactants to provide rapid wetting.

The inert extenders which are preferred for use in the wettable powdersof this invention containing the active compounds are of mineral ororganic origin.

Extenders suitable for the wettable powder formulations of thisinvention are the natural clays, vermiculite, diatomaceous earth, andsynthetic mineral fillers derived from silica and silicate. Mostpreferred filters for this invention are kaolinites, attapulgite clay,montmorillonite clays, synthetic silicas, synthetic magnesium silicate,and calcium sulfate dihydrate. A surface active agent can also be addedto give a homogenous and stable formulation.

Among the more preferred surfactants are the nonionic and anionic types.They are most suitable for the preparation of dry, wettable products ofthis invention and dispersants. Occasionally a liquid, non-ioniccompound which is primarily an emulsifier may serve as both wetter anddispersant.

Most preferred wetting agents are alkylbenzene and alkylnaphthalenesulfonates, sulfated fatty alcohols, amines, or acid amides, long chainesters of sodium isethionate, esters of sodium sulfosuccinate, sulfatedor sulfonated vegetable oils, and ditertiary acetylenic glycols.Preferred dispersants are methyl cellulose, polyvinyl alcohol, ligninsulfonates, polymeric alkylnaphthalene sulfonates, sodium naphthalenesulfonates, polymethylene bisnaphthalene sulfonate, andsodium-N-methyl-N-(long chain acid) taruates.

Wetting and dispersing agents in these preferred wettable powdercompositions of the invention are usually present at concentrations offrom about 0.5 weight percent to 5 weight percent. The inert extenderthen completes the formulation. Where needed, 0.1 weight percent of theextender may be replaced by a corrosion inhibitor or an anti-foamingagent or both.

Thus, wettable powder contains a corrosion inhibitor or an anti-foamingagent or both, the corrosion inhibitor should not exceed about 1 percentof the composition, and the anti-foaming agent should not exceed about0.5 percent by weight of the composition, both replacing equivalentamounts of the inert extender.

B. Dusts. Dusts are dense powder compositions which are intended forapplication in dry form. Dusts are characterized by their free-flowingand rapid settling properties so that they are not readily windborne toareas where their presence is not desired. They contain primarily anactive ingredient and a dense, free-flowing, solid extender. Theirperformance is sometimes aided by the inclusion of a wetting agent andconvenience in manufacture frequently demands the inclusion of an inertabsorptive grinding aid.

The wettable powder as described above can also be used in thepreparation of dusts. While such wettable powders can be used directlyin dust form, it is more advantageous to dilute them by blending withthe dense dust diluent. In this manner, dispersing agents, corrosioninhibitors, and anti-foam agents may also be used as components of adust.

Thus, the dust compositions of this invention can comprise from about0.5 to 20.0 weight percent active ingredient, 5 to 25 weight percentfiller, 0.0 to 1.0 weight percent wetting agent, and from about 30 to 90weight percent dense, free-flowing extender, as these terms are usedherein. Such dust formulations can contain, in addition, minor amountsof dispersants, corrosion inhibitors, and anti-foam agents derived fromthe wettable powders used to make the dust.

C. Emulsifiable oils. Emulsifiable oils are usually solutions orsuspensions of active material in non-water miscible solvents togetherwith a surfactant and/or emulsifier.

For compositions of this invention, emulsifiable oil compositions can bemade by mixing the active ingredient with an organic solvent andsurfactant. Suitable solvents for the compositions of this invention arechlorinated solvents, water immiscible ethers, esters, or ketones aloneor in admixture with aromatic hydrocarbons. Suitable surfactants arethose ionic or non-ionic agents known to the art as emulsifying agents.

Emulsifying agents most suitable for the emulsifiable oil compositionsof this invention are long chain alkyl or mercaptan polyethoxy alcohols,alkylaryl polyethoxy alcohols, sorbitan fatty acid esters,polyoxyethylene ethers with sorbitan fatty acid esters, polyethyleneglycol esters with fatty rosin acids, fatty alkylol amide condensates,calcium and amine salts of fatty alcohol sulfates, oil soluble petroleumsulfonates, or preferably mixtures of these emulsifying agents shouldcomprise from about 1 to 10 weight percent of the total composition. Asdescribed above, however, up to 5 parts of emulsifying agent for eachpart of active ingredient can be used.

Thus, emulsifiable oil compositions of the present invention can consistof from about 10 to 50 weight percent active ingredient, about 40 to 82percent solvents, and about 1 to 10 weight percent emulsifier, as theseterms are defined and used above.

D. Granules. Granules are physically stable, particulate compositionscontaining spores and/or mycelia of this invention which adhere to orare distributed through a basic matrix of a coherent, inert carrier withmicroscopic dimensions. In order to aid leaching of the activeingredient from the granule, a surfactant can be present.

The inert carrier is preferably of mineral origin, and suitable carriersare natural clays, some pyrophyllites and vermiculite. Suitable wettingagents can be anionic or non-ionic.

For the granule compositions of this invention, most suitable carriersare to two types. The first are porous, absorptive pre-formed granules,such as preformed and screened granular attapulgite or heat expanded,granular, screened vermiculite. On either of these, a solution of theactive agent can be sprayed and will be absorbed at concentrations up to25 weight percent of the total weight. The second type are initiallypowdered kaolin clays, hydrated attapulgite, or bentonite clays in theform of sodium calcium, or magnesium bentonites. Water-soluble saltssuch as sodium salts may also be present to aid in the disintegrationsof the granules in the presence of moisture. These ingredients areblended with the active component distributed uniformly throughout themass. Such granules can also be made with 25 to 30 weight percent activecomponent but more frequently a concentration of about 10 weight percentis desired for optimum distribution. The granular compositions of thisinvention are believed to be most useful in a size range of 15–30 mesh.

The most suitable wetting agents for the granular compositions of thisinvention depend upon the type of granule used. When pre-formed granulesare sprayed with active material in liquid form, the most suitablewetting agents are non-ionic, liquid wetters miscible with the solvent.These are more generally known in the art as emulsifiers and comprisealkylaryl polyether alcohols, alkyl polyether alcohols, polyoxethylenesorbitan fatty acid esters, polyethylene glycol esters with fatty orrosin acids, fatty alkylol amide condensates, oil petroleum or vegetableoil sulfonates, or mixtures of these. Such agents will usually compriseup to about 5 weight percent of the total composition.

When the active ingredient is first mixed with a powdered carrier andsubsequently granulated, liquid non-ionic wetters can still be used, butit is usually preferable to incorporate at the mixing stage one of thesolid, powdered anionic wetting agents such as those previously listedfor the wettable powders. Such agents should comprise about 0 to 2percent of the total composition.

Thus, the preferred granular formulation of this invention comprisesabout 5 to 30 weight percent active material, about 0 to 5 weightpercent wetting agent, and about 65 to 95 percent inert mineral carrier,as these terms are used herein.

A further aspect of the subject invention pertains to containers inwhich the compositions of the subject invention are sold and/ordistributed. In a preferred embodiment, these containers contain theplant essential oil formulations and have instructions for the use ofthe essential oils for the control of plant pathogens. In a preferredembodiment, the containers are plastic (or other appropriate inertmaterial). The formulation is preferably concentrated but may also bediluted for immediate use. In a preferred embodiment, the instructionspertain to the use of the plant essential oils as fumigants for thecontrol of plant pests. In a further preferred embodiment, theinstructions for use are written on the outside of the container.

Example 5 Specific Formulations

Specific formulations which can be used according to the subjectinvention as bio-fumigants for field application include the following:

-   -   UFBF771: 8 ml Pure Cymbopogon Martini Oil, 2 ml 95% Ethyl        alcohol, 1 ml detergent, 9 ml water (total volume of 20 ml).

UFBF772: 8 ml Pure Melaleuca Altemifolia Oil, 2 ml 95% Ethyl alcohol, 1ml detergent, 9 ml water (total volume of 20 ml).

UFBF773: 8 ml Pure Cymbopogon Flexuosus Oil, 2 ml 95% Ethyl alcohol, 1ml detergent, 9 ml water (total volume of 20 ml).

UFBF774: 8 ml Pure Eucalyptus Citriodora Oil, 2 ml 95% Ethyl alcohol, 1ml detergent, 9 ml water (total volume of 20 ml).

A person skilled in the art, having the benefit of the instantdisclosure could readily prepare various volumes of the pesticidalcomposition described herein.

Pure essential oils can be readily purchased. Based on theseformulations (mixture of essential oils with other ingredients asneeded), a stable emulsion can be readily prepared and applied with aninjector.

These compositions are effective against soil-borne fungi such asFusarium, Pythium, Phytophthora and Sclerotium rolfsil and bacterialwilt (Ralstonia solanacearum). Nematodes can also be treated.

Example 6 Specific Protocol for Field Use

In a specific embodiment, the bio-fumigants can be applied using singleinjector to a 30 cm depth. A total volume of 20 ml can be applied toevery 30 cm of the soil covered with plastic mulch.

The following procedure can be used for field application includingsmall plot field experiments:

-   -   1) Cover the beds with plastic mulch.    -   2) Open small holes every 15 inch. With an injector, liquid        formulation can be injected.    -   3) The openings can be sealed immediately for at least 15 days.    -   4) Open the holes for transplants, wait 10 days before        transplanting.

A total of 25 days can be left between application and planting.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication and the scope of the appended claims.

1. A method for reducing damage to tomato plants caused by Ralstoniasolanacearum wherein said method consists essentially of applying tosoil, as a fumigant, a composition consisting essentially of thymol,ethanol and a detergent, wherein the concentration of ethanol is atleast 1%, wherein tomato plants are planted in the soil within 25 daysof the application of the fumigant to the soil, and wherein the use ofsaid fumigant results in an increase in the market basket of tomatoesdue to the control of Ralstonia solanacearum without phytotoxicity tothe tomato plants.